Radial ball bearings 1 such as illustrated in FIG. 21 are assembled in rotary member support sections of various kinds of rotating equipment. As a radial ball bearing 1, a single-row deep-groove radial ball bearing is used in which a plurality of balls 4 are rotatably provided between an outer ring 2 and an inner ring 3 that are concentric with each other. A deep-groove outer-ring raceway 5 is formed around the entire circumference of a middle portion in the axial direction of the inner-circumferential surface of the outer ring 2, and a deep-groove inner-ring raceway 6 is formed around the entire circumference of a middle portion in the axial direction of the outer-circumferential surface of the inner ring 3. With the plurality of balls 4 that are held by a cage 7 rotatably provided between the outer-ring raceway 5 and the inner-ring raceway 6, the outer ring 2 and inner ring 3 freely rotate relative to each other.
A low cost method for manufacturing bearing rings such as the outer ring 2 and the inner ring 3 of a radial ball bearing 1 such as described above is disclosed in JP2009-279611 (A). In this method, first, in a state in which the outer diameter of a bottom-end section of a circular column-shaped billet 8 illustrated in FIG. 22A is restrained, by crushing the billet 8 in the axial direction by performing an upsetting process on the billet 8, a first intermediate blank 11 having small-diameter section 9 and large-diameter section 10 such as illustrated in FIG. 22B is formed. Next, by processing the small-diameter section 9 into a small-diameter second cylindrical section 12 by performing a forward extrusion process on the small-diameter section 9, a second intermediate blank 13 as illustrated in FIG. 22C is obtained. Then, by further processing the large-diameter section 10 into a large-diameter first cylindrical section 14 by performing a rear extrusion process on the large-diameter section 10, a third intermediate blank 15 as illustrated in FIG. 22D is obtained. After that, by punching out a bottom-plate section 16 of the third intermediate blank 15 by performing a punching process on the third intermediate blank 15, a fourth intermediate blank 17 as illustrated in FIG. 22E is obtained. Then, as illustrated in FIG. 22F, a small-diameter cylindrical member 18 is obtained by punching out a portion that corresponds to the second cylindrical section 12 from the fourth intermediate blank 17 by performing a punching process on the fourth intermediate blank 17. Finally, as illustrated in FIG. 22G, a large-diameter cylindrical member 20 is obtained by punching out an inward-facing flange section 19 from a portion that corresponds to the first cylindrical section 14. Both the small-diameter cylindrical member 18 and large-diameter cylindrical member 20 that are obtained in this way are annular shaped metal members.
The small-diameter cylindrical member 18 is the blank for the inner ring 3, however, an inner-ring raceway 6 is not formed around the outer-circumferential surface of the small-diameter cylindrical member 18, and the outer diameter dimension, the axial-direction dimension, and the shape of the inner-circumferential surface and the outer-circumferential surface are not the dimensions and shape of the inner ring 3. Moreover, the large-diameter cylindrical member 20 is the blank for the outer ring 2, however, an outer-ring raceway 5 is not formed around the inner-circumferential surface of the large-diameter cylindrical member 20, and the inner-diameter dimension, the outer-diameter dimension, the axial-direction dimension, and the shape of the inner-circumferential surface and the outer-circumferential surface are not the dimensions and shape of the outer ring 2. Performing work to process the small-diameter cylindrical member 18 into the shape of the inner ring 3, and to process the large-diameter cylindrical member 20 into the shape of the outer ring 2 by a rolling process is disclosed in JP2009279611 (A) and JPS59212142 (A).
FIG. 23 and FIG. 24 illustrate a manufacturing apparatus 21 for a ring-shaped member as disclosed in JPS59212142. The manufacturing apparatus 21 is an apparatus for processing annular shaped metal blank 26 such as the small-diameter cylindrical member 18 into a ring-shaped member 22 such as the inner ring 3 by performing a rolling process, and includes a mandrel 23, a forming roll 24, and a support roll 25.
The mandrel 23 has a first rolling surface 27 for performing a rolling process on the inner-circumferential surface of the metal blank 26, and a pair of cylindrical surface shaped mandrel-side regulating surfaces 28 that are provided on both sides in the axial direction of the first rolling surface 27. The first rolling surface 27 is such that the middle portion in the axial direction has a cylindrical surface shape (cross-sectional linear shape) of which the outer diameter does not change with respect to the axial direction, and the portions near both ends in the axial direction have cross-sectional arc shapes of which the outer diameter becomes larger going toward both ends in the axial direction. The mandrel 23 is supported by a cradle 29 so that displacement in the axial direction (up-down direction in FIG. 23 and FIG. 24), and rotation around the center axis of the mandrel 23 are possible.
The forming roll 24 has: a second rolling surface 30 that has a cylindrical shape and is formed around the middle section in the axial direction of the outer-circumferential surface, and is for performing a rolling process on the outer-circumferential surface of the metal blank 26; and a pair of cylindrical surface shaped forming-roll-side regulating surfaces 31 that are formed on both side in the axial direction of the second rolling surface 30. The second rolling surface 30 is such that the portions near both ends in the axial direction have a cylindrical surface shape (cross-sectional linear shape) of which the outer diameter does not change in the axial direction, and the portion near the center in the axial direction has a cross-sectional arc shape of which the outer diameter becomes larger going toward the center in the axial direction. The forming roll 24, is such that in a state in which the center axis of the forming roll 24 is parallel with the center axis of the mandrel 23, the second rolling surface 30 is made to face the first rolling surface 27 of the mandrel 23. The forming roll 24 is able to displace (move toward or away from the mandrel 23) in the horizontal direction (left-right direction in FIG. 23 and FIG. 24) while rotating.
The support roll 25 includes a pair of rollers 32 that arranged with a specified space in the axial direction provided in between. The support roll 25 is provided on the opposite side of the forming roll 24 with respect to the center axis of the mandrel 23 so that the center axis of the support roll 25 is parallel with the center axis of the mandrel 23, and part of the outer-circumferential surface of the roller 32 is made to face the mandrel-side regulating surface 28. The rotating shaft of the forming roll 24 and the rotating shaft of the support roll 25 are coupled together by a synchronizing mechanism 33, and the forming roll 24 and support roll 25 are able to rotate in synchronization, being rotated and driven by an electric motor 34.
Next, the procedure for manufacturing the ring-shaped member 22 by performing a rolling process on the metal blank 26 using the manufacturing apparatus 21 for a ring-shaped member will be explained with reference to FIG. 24. First, as illustrating in FIG. 24A, in a state in which the mandrel 23 is inserted into the space in the radial direction of the metal blank 26, part in the circumferential direction of the metal blank 26 is arranged between the first rolling surface 27 of the mandrel 23 and the second rolling surface 30 of the forming roll 24. Part in the circumferential direction of the outer-circumferential surface of the pair of rollers 32 of the support roll 25 are made to closely face the pair of mandrel-side regulating surfaces 28 of the mandrel 23.
Next, in a state in which the forming roll 24 and the support roll 25 are rotated and driven by rotating and driving the electric motor 34, the forming roll 24 is made to displace in a direction toward the mandrel 23 (toward the left side in FIG. 23 and FIG. 24). As a result, the outer-circumferential surface of the forming roll 24 comes in contact with the outer-circumferential surface of the metal blank 26, which causes the metal blank 26 to rotate. As the forming roll 24 is made to displace further toward that mandrel 23 from the state of contact between the outer-circumferential surface of the forming roll 24 and outer-circumferential surface of the metal blank 26, the mandrel 23 is pressed by way of the metal blank 26, and the outer-circumferential surface of the mandrel 23 comes in contact with the outer-circumferential surfaces of the pair of rollers 32 of the support roll 25. In a state in which the outer-circumferential surface of the mandrel 23 is in contact with the outer-circumferential surface of the rollers 32, the mandrel 23 is made to rotate due to the rotation of the rollers 32. In this state in which the outer-circumferential surface of the mandrel 23 is in contact with the outer-circumferential surface of the rollers 32, the support roll 25 supports the mandrel 23 so that the mandrel 23 does not displace toward the left side in FIG. 23 and FIG. 24.
As the forming roll 24 is made to further displace in a direction toward the mandrel 23 from a state in which the outer-circumferential surface of the mandrel 23 is in contact with the outer-circumferential surface of the rollers 32, part in the circumferential direction of the metal blank 26 is pressed in between the forming roll 24 and the mandrel 23 that is supported by the support roll 25, and at the same time that the first rolling surface 27 of the mandrel 23 is rolled over the inner-circumferential surface of the metal blank 26, the second rolling surface 30 of the forming roll 24 is rolled over the outer-circumferential surface of the metal blank 26. As this kind of rolling process is performed, the outer-diameter dimension and the axial-direction dimension of the metal blank 26 increase. When the forming-roll-side regulating surface 31 of the forming roll 24 comes in contact with the mandrel-side regulating surface 28 of the mandrel 23, displacement of the forming roll 24 in the direction toward the mandrel 23 is stopped, and the rolling process ends. The inner ring 3 is obtained by performing a cutting process, a grinding process and a finishing process on the ring-shaped member 22 that was obtained by this kind of rolling process.
With this kind of manufacturing method for a ring-shaped member, it is possible to make the processing apparatus more compact than in the case of manufacturing a ring-shaped member 22 by performing a forging process on the metal blank 26, and it is possible to make the machining allowance small when performing a cutting process and a turning process, so it is possible to reduce the equipment cost and material cost. However, in this kind of manufacturing method, means for regulating the outer-diameter dimension of the ring-shaped member are not provided, so there is a possibility that variation in the shape (outer-diameter dimension and axial-direction dimension) of the ring-shaped member 22 will occur due to variation in the outer-dimensional shape of the metal blank 26 or due to variation in the assembled state of the metal blank 26 in a processing apparatus. When variation in the shape of the ring-shaped member 22 occurs, there is a possibility that the finishing process (cutting process and grinding process) will become troublesome, and that manufacturing costs will increase.
In JPH07275990 (A), technology is disclosed in which variation in the shape of a ring-shaped member is prevented by using a metal die that is capable of regulating the outer-diameter dimension and axial-direction of a ring-shaped member after a rolling process. However, in this technology, when the volume of the metal blank being used is larger than a specified value, the molding space of the metal die will become filled by the metal blank in a step before pressure by the forming roll is finished, and there is a possibility that the internal stress on this metal blank will become to high, and that it will become easy for damage to the mandrel to occur. Even when the mandrel is not damaged, the metal blank which had no place to go in the molding space of the metal die is distorted and thus there is a possibility that the roundness of the ring-shaped member becomes bad. When there is damage to the mandrel or when the roundness of the ring-shaped member becomes bad, there is a possibility that a change in volume of the metal blank will occur due to a temperature change in the metal die.